This invention relates to countercurrent extraction methods and in particular, to a means for separating gaseous elements from the liquid phase components of a waste gas stream.
Removal of gaseous radioactive iodines and other elemental species from a waste gas stream to prevent their entrance to the atmosphere is of considerable importance. It is primarily by such means that one can prevent the contamination of surfaces to which these substances may adhere and also to prevent ingestion by humans and animal life. The radioactive gaseous elements of concern here can include inorganic species such as various elemental substances, as well as organic species such as methyliodide which may be present in waste gases which may comprise radioactive off gases from nuclear fuel reprocessing plants. These radioactive materials are formed in the nuclear reactor fuel by the fission of the fuel material. If these off gases can be individually collected from the gaseous effluent, they might possibly be used for other unrelated purposes.
Various means have been used in the past for filtering out and/or trapping such radioactive materials in the off gas stream, for example, materials such as copper and other metals which react with iodine have been used to adsorb the iodine that is not stopped by mechanical filtration. Silver nitrate supported on an inert substrate reacts with the iodine species to form silver iodide. Another material commonly used in cleanup systems of reactor containment atmospheres for fission products is charcoal impregnated with iodine and potassium iodide. Various inefficiencies and limitations in the use of these different means for separating such effluent gaseous mixtures into their component gases have indicated the need for a more versatile and more efficient means of separating the individual gases from the effluent.